'baff' originates from Scots dialect, used historically in northern English and Scots speech to denote actions like 'to strike' or 'to bathe'.

'baff' appears in Middle English and Scots forms such as 'baffen' (or similar dialectal spellings) and remained primarily a regional/dialectal verb into modern English as 'baff'.

Initially it covered senses like 'to beat' and 'to wash' in regional speech; over time the word remained regional and the senses have been preserved in dialect usage rather than entering standard modern English.